Implement PNOJ API

[HillcrestEnigma]

PNOJ should have an API endpoint for people to access the data hosted by PNOJ or submit new data programmatically.
To future-proof the API, GraphQL would be preferable.
Bulk rejudging submissions and rescoring submissions and users should be done through the API.
The API would also allow for a command-line client to exist to assist the user.

List of things that should the API should support:

• Authenticate using API tokens, if unauthenticated, return data accessible by normal users
• Fetch Problems, Users, Submissions, Organizations, Comments, OrganizationRequests
• Fetch Submission status and source
• Fetch last viewed problem by a user
• Rejudge or Rescore Submissions
• Rescore Users
• Create Problems, Submissions, Comments
• Rate-limit access